The goal of this proposal is to examine the role of the steroid-hormone ecdysone pathway in the differentiation of the Drosophila eye. The activity of the E75 ecdysone-inducible gene will serve as the investigative focus. Examination of known and induced E75 mutants will allow for the characterization of the abnormal photoreceptor growth phenotype. The epistatic relationship between the function of ecdysone and that of other signaling pathways necessary for eye development will be conducted by ectopic expression of various developmental genes, including E75, in both wild-type and developmentally-mutant flies. integration of the ecdysone inducible pathway with other signaling methods used in the eye, including the EGF-R pathway, will elucidate a developmental interaction between steroid hormone and growth factor signaling pathways. Evidence exists for interaction between hormone-regulated transcription factors and the EGF-R pathway in both mammals and insects. In humans, steroid-hormone control may be involved in mediating increased EGF production in breast-cancer tumors, as well as other cancers. Examination in a system as thoroughly studied as the Drosophila compound eye will allow rapid insight into the methods of this interaction, and is essential for further knowledge regarding human development and some types of cancerous disease.